Hydrophilic or soft contact lenses are mainly produced from water-absorbable plastic materials such as 2-hydroxymethacrylate (HEMA) which may be crosslinked with a tetra-functional monomer such as ethylene glycol dimethacrylate as disclosed in U.S. Pat. No. 3,988,274. Soft contact lenses produced from water-absorbable plastic materials such as HEMA are also disclosed in U.S. Pat. No. 3,813,447; 4,252,421 and 3,988,274.
Attempts have been made to color these soft contact lenses for the purpose of enhancing the aesthetic beauty of the eye of the wearer of the colored lens. One prior art technique is to paint or print a colored portion onto a soft contact lens using an implement such as a brush, as disclosed in Contact Lens Forum, Volume 3, No. 8, August, 1978, page 89. Another technique involves the cementing of a colored covering layer onto a clear hydrogel lens, as disclosed in U.S. Pat. No. 3,679,504.
There are, however, several problems with this type of surface coloring technique. First, the color is printed on the lens after it has been manufactured and, therefore, is not uniformly dispersed through the lens material itself. As a result, the color tends to fade and chip away after repeated use. Also, it is necessary to first manufacture the clear lens and fit it on the patient's eye before the coloring takes place. This requires the lens to be sent back to the manufacturing company by the patient's doctor. Moreover, surface coloring inhibits gas permeability, i.e., the transmission of oxygen to the cornea. Finally, the surface coloring process requires additional fabrication steps and equipment.
Coloring of soft contact lenses has also been performed by dispersing water soluble and water insoluble dyes throughout the plastic material which makes up the lens. For example, U.S. Pat. No. 4,252,421 discloses a soft contact lens having a tinted central core which is colored by means of a dye that is dispersed throughout the core and an outer lens element which is usually clear. The colored central core is formed from a tinted button which in turn is polymerized from a co-monomer mixture which includes a dye. The dye may be of two types: water insoluble or polymer bound.
U.S. Pat. No. 4,157,892 discloses a somewhat similar method of producing a colored soft contact lens. Thus, the patent discloses a method of coloring water-absorbable plastic by developing an azoic dye within the hydrophilic contact lens. The water absorbable plastic material containing a coupler is mixed with a diazonium compound in a suitable solvent at optimum pH to produce an azoic dye.
Lenses produced by such dying methods also possess a number of disadvantages. Specifically, the dye in the plastic lens material is not migration proof and, as a result, tends to streak and run out of the lens. Moreover, the dyed lenses are transparent and accordingly cannot be used to change the appearance of the wearer's eye color from one color to another color.
In addition to the use of dyes to color soft contact lenses, pigments have been dispersed in the soft contact lens material in an effort to produce an acceptable lens. These efforts, however, have been ineffective. When attempted with spun-cast soft lenses, little or no pigment has remained properly dispersed in the body of the lens; and when attempted with lenses made by stationery casting and machining (a "lathe cut lens"), such lenses do not have a satisfactorily evenly dispersed color when made in commercial production quantities.
Another area where pigments have been dispersed in an ethylenically unsaturated polymerizable compound is in the manufacture of paint. For example, U.S. Pat. No. 4,234,466 discloses a polymerizable composition containing an ethylenically unsaturated polymerizable compound, a resin and a pigment. The disclosed composition is, however, unsuitable for the production of pigmented hydrophilic contact lenses since the required high degree of pigment dispersion cannot be achieved, while low amounts of pigment failed to result in sufficient coloring.
It is therefore among the objects of the present invention to provide a pigmented water-absorbable plastic material in which low amounts of pigment are evenly dispersed and non-migrating.
It is also among the objects of the present invention to provide a pigmented water-absorbable plastic material useful in the production of colored soft contact lenses.